Given the great strides that Ethernet and InfiniBand networking have made in the past decade, you would think that there wasn't much room for proprietary interconnects linking together nodes in parallel supercomputers. Oddly enough, despite the overwhelming popularity of these two increasingly similar networking technologies, …
Teradata has had a proprietary interconnect since the 1980's:
The current bynet is scalable, resilient and load balanced. As the system is scaled-out though the deployment of more SMP nodes the bynet bandwidth increases. This is essential in order to maintain overall system performance.
For my money though, the real 'smarts' lie in the bynet's ability to perform final aggregation and sort processing on-the-fly within the interconnect fabric, without impacting the DBMS nodes.
Parallel databases lacking this capability ship partial result sets to a master node to perform the same function - there is still an interconnect, it's just not smart.